THE PULSE. 



327 



compelled to resort to other means to ascertain its condition. One 

 of the best sources of information is the pulse. This he studies 

 to learn : (1) The frequency of the heart-beats, for each time the 



FIG. 171. Scheme of Marey's sphygmograph : a, toothed wheel connected with 

 axle h, and gearing into toothed upright 6 ; c, ivory pad which rests over blood- 

 vessel and is pressed on it by moving g, a screw passing through the spring j ; e, 

 writing-lever attached to axle h, and moved by its rotation ; e writes on d, a travel- 

 ling surface moved by clockwork /. 



ventricle contracts there is a corresponding beat of the pulse ; (2) 

 *the force with which the heart is acting, for the strength of the 

 pulse is an indication of that of the heart; (3) its regularity; and 



FIG. 172. Sphygmogram from a normal human radial pulse beating from 58 to 60 

 times a minute. To be read from left to right (Burdon-Sanderson). 



(4) its tension i. e., whether it is compressible or not, whether a 

 slight pressure will obliterate it, or whether it requires a greater 

 amount of pressure. Low tension implies low arterial pressure, 

 and high pressure denotes high blood-pressure. 



FIG. 173. Pulse-tracings : 1, primary elevation ; 2, predicrotic or first tidal wave ; 

 3, dicrotic wave. The depression between 2 and 3 is the dicrotic or aortic notch ; 3 

 is better marked in B than in A. C, dicrotic pulse with low arterial pressure. D, 

 pulse with high arterial pressure-summit of primary elevation in the form of an 

 ascending plateau. E, systolic anacrotic pulse; the secondary wavelet a occurs 

 during the upstroke corresponding to the ventricular systole. F, presystolic ana- 

 crotic pulse; a occurs just before the systole of the ventricle. In this rarer form 

 of anacrotism a may sometimes be due to the auricular systole when the aortic 

 valves are incompetent (Stewart). 



The Sphygmograph (Fig. 171). This instrument makes 

 a record, sphygmogram or pulse-trace, of the pressure in the 



